SXS
I have had a couple of 2-1/2 English and Scottish 16 gauge guns. I opened the chambers on one of them, and now know that was a mistake. My current 2-1/2" 16 is a lightweight Harkom, and I load low pressure 2-3/4" 1 oz. 16 bore loads - under 7000 PSI. They work just fine, and anything heavier would be painful in a 5-1/2 lb. gun.
I have also used the Polywad Vintagers, but they are limited to 7/8 oz. of shot, enough for most of my shooting, but not all.
Reaming chambers on British proofed 2-1/2" guns used to be common practice in the US, but is not considered correct now. The gun will be out of proof, and many smiths will advise against it. There is also the issue of removing metal forward of the original chambers and being left with less margin of safety.
